Posted by Blair Friesen, Last modified by Blair Friesen on 30 September 2016 02:12 PM

The "Sum of Grades" aggregation has been removed and replace with "Natural Weighting." Long-term, Moodle intends to remove the other forms of aggregation, as people get used to using the new (and easier to understand) "Natural Weighting" aggregation method. So, it's worth learning about! We (DL Support) will likely provide a workshop on how to convert your course to this grading method, sometime in the late summer or fall.

Rationale

In grading, weight is the proportion of an item's value in relation to all the other items in its container (category or course).

Value is most often represented as 'points'.

Every grade has a weight.

There are three fundamental approaches to dealing with weighting in a gradebook.

Simple (or natural) weighting, maximum points earnable for each item are appropriately in relation to one another. Example - If you have two items in a category, one worth 10 points and the other worth 30, then item 1 is 25% (10/40) and item 2 is 75% (30/40).

Adjusted weighting. Users often want to adjust categories and even items to have a weight other than the natural weight, essentially ignoring the points entirely. An example would be, Quizzes=40%, Assignments=50%, Attendance=10%.

Mean of grades. If I have a category made up of five quizzes all worth different points and I want a category percentage to just tell the average (or mean) of all the quiz results' percentage correct, I would choose this approach again, disregarding the points.

Simplifying the understanding of weighting reduces the aggregation methodology down to 'either/ or'

either 'leave weights as is -- natural'

or 'adjust to suit my needs -- adjusted weights'

This greatly simplifies the interface needed to present these options

They don't need to select an aggregation type

They don't need to know how each aggregation type performs

The actual weight of every item and category is always displayed to them.

If those are not the weights they want, they merely adjust them.

Much easier for the common user to grasp.

This interface and calculations are expected to suit the needs of all except very edge cases (which can still be handled with formulas). If it turns out that this is enough for everyone then we can potentially remove quite a lot of aggregation code from the gradebook at a later stage, improving speed and readability.

How natural weights meets the requirements of the aggregation types

Sum of grades

Moodle determines the "natural weights" for this by default based on point values.

Mean of grades

Set all weights equal to each other. Doesn't matter what the number is, as in legacy behavior Moodle will automatically adjust so the sum equals 100%. However, in this implementation the group wants to have a pop-up warning the user the weights don't add up to 100% and they will therefore be adjusted uniformly to equal 100%.

Weighted mean of grades

Adjust weights as desired. No change from current behavior.

Simple weighted mean of grades

Leave all weightings as is, no change necessary. Same as Sum of grades.

Mean of grades (with extra credits)

Extra credit has a natural weight that takes the total container (category/ course) weight above 100% (hence, 'extra'). Extra credit is available at all times no matter what scheme of weighting is chosen.

Highest

User would input the value '1' for 'Keep highest' in the category

Lowest

Of doubtful use. Not possible using natural weights, but it can also be done by a calculation into a new item.

Median / Mode of grades

Not possible using natural weights, but it's doubtful anyone uses these anyway so perhaps this can be deprecated entirely.

Here's a short video explanation of the Moodle 2.8 Gradebook Natural Method by Humboldt State University: